D-Psicose (Psi), the C3-epimer of D-fructose (Fru), is a noncalorie sugar with a lower glycemic response. The trans-cellular pathway of Psi in human enterocytes was investigated using a Caco-2 cell monolayer. The permeation rate of Psi across the monolayer was not affected by the addition of phlorizin, an inhibitor of sugar transporter SGLT1, whereas it was accelerated by treatment with forskolin, a GLUT5-gene inducer, clearly showing that GLUT5 is involved in the transport of Psi. The permeability of Psi was suppressed in the presence of D-glucose (Glc) and Fru, suggesting that the three monosaccharides are transported via the same transporter. Since GLUT2, the predominant sugar transporter on the basolateral membrane of enterocytes, mediates the transport of Glc and Fru, Psi might be mediated by GLUT2. The present study shows that Psi is incorporated from the intestinal lumen into enterocytes via GLUT5 and is released to the lamina propria via GLUT2.
The present study examined the effects of milk protein hydrolysates made by the enzymatic hydrolysis of milk protein during milk fermentation. Two kinds of lactic acid starter, YC-280 (Lactobacillus bulgaricus and Streptococcus thermophilus) and ABT-1 (Lactobacillus acidophilus, Streptococcus thermophilus and Bifidobacterium bifidum BB-12) were used. Fermentation time, the production of EPS, syneresis, hardness and the viability of the bacteria were measured. The effects were different between the various milk protein hydrolysates. The addition of casein hydrolysate and whey protein hydrolysate shortened the fermentation time and increased the production of EPS ; furthermore, it reduced the syneresis and hardness of milk fermented by ABT-1. However, only whey protein hydrolysates exhibited these effects when fermentation was conducted using YC-280. These results suggest that the peptides and amino acids in milk protein hydrolysates stimulate the metabolism of lactic acid bacteria and increase EPS production, thus reducing syneresis and hardness. The effects were different depending on the hydrolysate or starter culture.
Clostridium cellulovorans produces multi-enzyme complexes called cellulosomes capable of efficiently degrading cellulosic biomass. There are three xylanase genes containing a sequence corresponding to a dockerin domain that are necessary for constructing cellulosomes in the genome. Among the xylanases encoded by these genes, xylanase B (XynB) contains a catalytic domain belonging to glycoside hydrolase family 10 and a carbohydrate-binding module (CBM) at the N-terminus, making it a member of CBM family 22. In this study, XynB was cloned, overexpressed, purified and crystallized. XynB was crystallized using the hanging-drop vapour-diffusion method in the presence of 0.2 M sodium acetate trihydrate, 0.1 M Tris-HCl pH 8.5, 32%(w/v) PEG 4000 at 293 K. X-ray diffraction analysis revealed that the crystal diffracted to 1.95 Å resolution and belonged to space group P222, with unit-cell parameters a = 74.28, b = 77.55, c = 88.20 Å, α = β = γ = 90°. The data-evaluation statistics revealed high quality of the collected data, thereby establishing a solid basis for determination of the structure of cellulosomal xylanase from C. cellulovorans.
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